Children can never be raised in a family because of one and very simple human emotion called greed. Children could only exist if we were emotionless, so I guess our species will quietly die out now.
Seriously though, there is a lot to humans, don't underestimate us. And insisting that our entire system be based on one single and pretty negative aspect of our characters, even if you think that aspect is immutable, is kinda sociopathic.